This invention relates to charging of a battery and, more particularly, to a microcomputer type battery charging controller using a microcomputer.
A battery such as a Ni-Cd battery is repeatedly used by being recharged. The battery in a discharged state is quickly charged from a direct current power source. When a fully-charged state is detected, the charging operation is changed over from quick charging to trickle charging. The battery is used again after being charged to a predetermined extent.
Recently, systems for charging a plurality of batteries have been used. Conventionally, necessary apparatuses provided separately from each other are combined to form this kind of system. In such a case, however, the number of component parts and the manufacture cost are increased and the size of the system is also increased.
To cope with this problem, a method of incorporating a microcomputer in a charging apparatus and controlling charging operations with the microcomputer has been practiced.
Properties of a battery are generally determined by materials of the battery. For example, Ni-Cd batteries have an electromotive force of about 1.2 V per unit cell and exhibit stable characteristics irrespective of the amount of remaining charge. With respect to batteries formed of the same materials, however, the number of cells connected in series and the current capacity vary greatly. For example, the number of cells connected in series generally ranges from 2 to 10.
Batteries varying in number of cells and current capacity are on the market and are used according to use. Various battery packs formed of a plurality of batteries combined are also used presently.
In a case where batteries varying greatly in charge current capacity are charged with a direct current power source at a constant current capacity, the differences between the charging characteristics of the batteries representing the changes in the voltage between the terminals with respect to charging time are substantially large. That is, one direct current power source can be used for a plurality of batteries of the same voltage, but the charging time varies with respect to different current capacities. However, the conventional microcomputer-controlled battery charging apparatuses are designed for a constant preset control.
Ordinarily, a battery is fully charged by detecting the absolute value of the voltage between its terminals and a reduction in voltage (-.DELTA.V) after formation of a peak. If these voltage values are set with a constant accuracy of, for example, 100 mV, fully-charged states are detected with largely different accuracies with respect to, for example, a two-cell battery and a ten-cell battery.
The conventional microcomputer-controlled battery charging apparatuses perform charging control under a constant predetermined condition.
Consequently, in the conventional charging system, the charging operation is not always performed in a suitable manner with respect to different types of batteries.